No problem, Mark! I've actually found a good answer, with hints from @vanakaru. I've been meaning to post here, but am still wrapped up in the creation of the show.
Basically, I bought a Matrox MXO2 Mini with ExpressCard to plug into my laptop and it works very well! If I want to also use it on my desktop production machine, all I have to do is buy the Matrox PCI card and then I have a solution that ports between any machine. It also works PC to MAC, so it's very flexible!
Matrox support is fantastic, by the way. Quite expert and they don't keep you on hold forever.
Hope this helps someone in the future.
Cheers,
Hugh